Electrochemical deposition method, electrochemical deposition apparatus, and microstructure

ABSTRACT

An electrochemical deposition method in which the structure of a substance to be deposited on the surface of a working electrode is determined, an electrochemical deposition apparatus, and a microstructure are provided.  
     A positive electrode  1  and a negative electrode  2  functioning as a working electrode are arranged oppositely in a liquid tank  5  containing an electrolytic (acid) solution (hereinafter referred to as “solution”)  4  in which plural substance are dissolved in an ionic state, and then a predetermined voltage is applied between the positive electrode  1  and the negative electrode  2.  A reference electrode  3  is also arranged in the liquid tank  5  and the potential between the negative electrode  2  and the reference electrode  3  is measured. Since the solution 4 can be considered as a conductor, the potential V 1  of the negative electrode 2 relative to the solution  4  can be determined. Furthermore, a reaction inhibitor is admixed in the liquid tank  5,  spontaneous electrochemical oscillation (current oscillation in this case) is generated in the electrochemical deposition reaction of the substances in the presence of the reaction inhibitor. The waveform of the electrochemical oscillation is controlled by regulating the potential V 1  of the negative electrode, the concentrations of the substances in the solution, and the kind and concentration of the reaction inhibitor, thereby the structure of a substance to be deposited on the surface of the working electrode is determined.

TECHNICAL FIELD

The present invention relates to an electrochemical deposition method inwhich a voltage is applied or a current is fed between plural electrodesimmersed in a solution in which an electrochemically depositablesubstance such as a metal is dissolved in an ionic state to deposit thesubstance on the surface of a working electrode, an electrochemicaldeposition apparatus, and a microstructure having lattices ranging insize from several tens to several hundreds of micrometers.

BACKGROUND ART

Through the progression of microfabrication technology, the propositionsof nanometer-size micro devices (nanodevices), as well as an increase inthe scale of integration, have been made. For example, researches onnanoperiodic structures of metals, semiconductors, conductive polymers,and so on are being conducted actively in various fields because variousfunctions such as giant magnetoresistance, tunnel magnetoresistance, andphotonics, emerge based on their characteristics. As methods for formingnanoperiodic structures, thin-film formation methods such as vapordeposition are established at present. These methods are multi-steptechniques in which objective substances are alternately laminated.

However, in the conventional techniques described above, there is aproblem that decrease in productivity and increase in cost areinevitable because those techniques each require a multi-step process.And further, it is inevitable that apparatuses for use in the formationof nanoperiodic structures are large in size, which further increasestheir production cost.

Therefore a self-organizing microfabrication technique called astructural formation based on nonlinear chemical dynamics is devised asa technique by which the above problems can be solved. This technique isa kind of bottom-up approach and is in an embryonic stage; however, itis expected as a technique which brings a drastic paradigm shift toconventional techniques.

Self organization includes static self organization and dynamic selforganization; a structure formed by the former is a thermal equilibriumstructure, i.e., a static ordered structure and is determined by theprinciples of intermolecular forces (interatomic forces) and equilibriumthermodynamics. On the other hand, a structure formed by the latter is apattern which is spontaneously formed in the flow of energy, that is, anordered structure which emerges in a non-equilibrium system andtherefore has various structures in itself in terms of time and space.Dynamic self organization has characteristics such as the manifestationof a drawing effect which static self organization does not exhibit, aself-recovery function, and a long-range interaction; if dynamic selforganization can be controlled, it becomes possible to manufacture amicrostructure having a desired structure.

Patent Document 1 discloses a method for manufacturing a laminated filmin which a conductive support is immersed in an aqueous solutioncontaining metal ions, the potential of the conductive support isoscillated by using the support as an electrode, and metal layers andmetal-oxide layers are alternately deposited on the conductive support.

Patent Document 1: Japanese Patent Application Laid-Open No.2002-129374

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, since the mechanism of the dynamic self organization has notyet been established and factors to be controlled required for thecontrol of the self organization has not yet been established, it hasbeen impossible to manufacture a microstructure having a desiredstructure. Put another way, it has been possible to manufacturemicrostructures as a result of the changing of manufacturing conditions,though it has been impossible to make them have desired structures. Inaddition, since the dynamic self organization is present in the flow ofenergy, there has been the problem that the interception of energysupplied from the outside results in the vanishment of the structures.

The present inventors conducted extensive studies on dynamicself-organization in an electrochemical reaction system. As a result,the studies have produced the finding that when microstructures aremanufactured by means of electrochemical oscillations (currentoscillations or potential oscillations), structures to be formed aredetermined based on the waveforms (such as periods and amplitudes) ofelectrochemical oscillations. With electrochemical reactions, it is easyto control them and even when energy has been intercepted, structurescan be accumulated as histories (deposits) and the traces of dynamicspace-time orders can be fixed and stored, thereby the structures formeddo not vanish. And furthermore, the inventors have made the finding thatthe waveform of electrochemical oscillation can be controlled in anautocatalysis process by selecting the kinds of substances to beelectrochemically deposited (for example, to be electrolyticallydeposited) and regulating the potential and current of a workingelectrode.

The present invention has been accomplished based on the above findings,and therefore an object of the invention is to provide anelectrochemical deposition method in which the structure of a substanceto be deposited on the surface of a working electrode is determinedbased on the waveform of electrochemical oscillation, i.e., currentoscillation or potential oscillation generated by applying a voltage orfeeding a current between plural electrodes immersed in a solution inwhich an electrochemically depositable substance such as a metal isdissolved in an ionic state and then controlling a potential of or acurrent into one electrode (called “working electrode”) of theelectrodes relative to the solution.

Another object of the invention is to provide an electrochemicaldeposition method in which the electrochemical oscillation is controlledby mixing a reaction inhibitor into the solution and then coupling anegative derivative resistance induced by the reaction inhibitor with apotential drop in the solution to produce an autocatalysis process.

Another object of the invention is to provide an electrochemicaldeposition method in which the structure of a substance to be depositedon the surface of the working electrode is determined by regulating theconcentration of the reaction inhibitor to control a potential of or acurrent into the working electrode at or with which electrochemicaloscillation occurs.

Another object of the invention is to provide an electrochemicaldeposition method in which the structure of a substance to be depositedon the surface of the working electrode is determined by using acationic surfactant with a carbon chain comprised of 10 carbon atoms ormore as a reaction inhibitor and regulating the length of the carbonchain to control the potential or the current at or with whichelectrochemical oscillation occurs.

Another object of the invention is to provide an electrochemicaldeposition method in which the structure of a substance to be depositedon the surface of the working electrode is determined by regulating theconcentration of the substance in the solution to control the waveformof electrochemical oscillation.

Another object of the invention is to provide an electrochemicaldeposition method in which when plural substances are dissolved in thesolution in an ionic state, the composition ratio of the structurecomprised of the substances is determined by controlling the waveform ofelectrochemical oscillation.

Another object of the invention is to provide an electrochemicaldeposition method in which when the structure of the deposited substancedetermined based on the waveform of the electrochemical oscillation is amulti-layered structure, the thickness and/or the composition ratio ofeach layer are determined by controlling the waveform of theelectrochemical oscillation.

Another object of the invention is to provide an electrochemicaldeposition method in which the structure of a substance to be depositedon the working electrode is determined based on the waveform ofelectrochemical oscillation generated by controlling the potential of orthe current into the working electrode such that the electrochemicaldeposition proceeds toward diffusion control.

Another object of the invention is to provide an electrochemicaldeposition method in which an upper potential or a lower potential isdetected at each oscillation of the electrochemical oscillation and thecurrent into the working electrode is controlled based on a variation inthe upper or lower potential such that the problem that the spontaneousoscillation ceases because the density of the current gradually lowersand then falls outside a range in which the spontaneous oscillationoccurs can be prevented and an electrochemical deposition apparatus.

Another object of the invention is to provide an electrochemicaldeposition method in which a microlattice structure with superiorevenness can be obtained by controlling an effective current density atthe working electrode relative to a current density in the solution suchthat the effective density is substantially constant to make the shapeof the microstructure grown on the surface of the working electrodeuniform.

Another object of the invention is to provide an electrochemicaldeposition apparatus capable of continuing the spontaneous oscillationby controlling the current into the working electrode such that thecurrent density at which the spontaneous oscillation occurs can besecured in order to prevent the problem that the spontaneous oscillationceases because the current density gradually lowers and then fallsoutside the range in which the spontaneous oscillation occurs.

Another object of the invention is to provide a microstructure which canbe produced as, for example, a high-strength electrode with an extremelylarge surface area whose crystallographically stable planes are exposedby using a substance deposited by using one of the above electrochemicaldeposition methods as a three-dimensional base structure and depositinganother substance on the surface of the substance.

Another object of the invention is to provide a microstructure having aninternal porous structure formed by polymerizing the surface of thesubstance deposited by using one of the above electrochemical depositionmethods and another substance to remove the deposited substance.

Means for Solving the Problems

An electrochemical deposition method according to a first aspect of thepresent invention is an electrochemical deposition method for depositingan electrochemically depositable substance on a surface of a workingelectrode by applying a voltage or feeding a current between a pluralityof electrodes immersed in a solution in which the substance is dissolvedin an ionic state, the method comprising:

generating electrochemical oscillation by controlling a potential of orthe current through the working electrode relative to the solution; and

depositing the substance with a predetermined structure according to awaveform of the electrochemical oscillation.

In this aspect of the invention, the plural electrodes are immersed inthe solution in which the electrochemically depositable substance (suchas a metal, a semiconductor, and a conductive polymer) is dissolved inthe ionic state and a voltage is applied or a current is fed between theelectrodes to electrochemically deposit the dissolved substance on thesurface of one electrode (the working electrode) of the electrodes. Atthe time of the electrochemical deposition, the spontaneouselectrochemical oscillation occurs by controlling the potential of orthe current into the working electrode relative to the solution. Sincethe waveform (for example, the period) of the electrochemicaloscillation can be controlled by controlling the potential of or thecurrent into working electrode, the structure of the substance to bedeposited on the surface of the working electrode can be determinedaccording to the waveform of the electrochemical oscillation. Since thestructure is self-formed through the self-organized oscillationphenomenon, individual portions of the structure are laminated in orderthrough the reflection of the history of the oscillation phenomenon.Therefore, the structure is accumulated as a history and the trace of adynamic space-time order can be fixed and stored, thereby the formedstructure does not vanish.

An electrochemical deposition method according to a second aspect of theinvention is further comprising:

mixing a reaction inhibitor into the solution; and

generating a state in which the reaction inhibitor attaches to thesurface of the working electrode and a state in which the reactioninhibitor detaches therefrom spontaneously and alternately.

In this aspect of the invention, the potential of or the current intothe working electrode at or with which the electrochemical oscillationoccurs is controlled by coupling a negative derivative resistanceinduced by the reaction inhibitor and a potential drop in the solutiontogether through the mixing of the reaction inhibitor into the solutionto produce an autocatalysis process, that is, to spontaneously andalternately bring about the state in which the reaction inhibitorattaches to the surface of the working electrode and the state in whichthe reaction inhibitor does not attach to the surface of the workingelectrode. The reaction inhibitor can be suitably mixed according tochemical reaction systems, which makes it possible to regulate the rangeof the potential of or the current into the working electrode at or withwhich the electrochemical oscillation occurs.

An electrochemical deposition method according to a third aspect of theinvention is characterized in that the potential of or the currentthrough the working electrode is controlled by regulating aconcentration of the reaction inhibitor such that the electrochemicaloscillation generates.

In this aspect of the invention, the potential of or the current intothe working electrode at or with which the electrochemical oscillationoccurs can be controlled by regulating the concentration of the reactioninhibitor. For example, in current oscillation as one form of theelectrochemical oscillation, a potential generated by the negativederivative resistance (the potential of the working electrode generatedwhen a current flowing into the working electrode abruptly decreases)can be shifted to the positive or negative side by regulating theconcentration of the reaction inhibitor in the solution. Specifically,by increasing the concentration of the reaction inhibitor, the potentialat which the current oscillation occurs can be shifted to the positiveside. It is clear from the above that the current oscillation occurs atthe potential generated by the negative derivative resistance andtherefore, when a reaction inhibitor of the same kind is used, thepotential at which the current oscillation occurs can be controlled byregulating the concentration of the reaction inhibitor, thereby thestructure of a substance to be deposited on the surface of the workingelectrode can be determined.

An electrochemical deposition method according to a fourth aspect of theinvention is characterized in that a cationic surfactant having a carbonchain consisting of 10 carbon atoms or more is used as the reactioninhibitor, and

the potential of or the current into the working electrode is controlledby regulating a length of the carbon chain such that the electrochemicaloscillation generates.

In this aspect of the invention, when the cationic surfactant with thecarbon chain comprised of 10 carbon atoms or more is used as thereaction inhibitor, the potential of or the current into the workingelectrode at or with which the electrochemical oscillation occurs can becontrolled by regulating the length of the carbon chain. For example, byregulating the length of the carbon chain, the potential effected by thenegative differential resistance can be shifted to the positive ornegative side. Specifically, by lengthening the carbon chain, thepotential at which the current oscillation occurs can be shifted to thepositive side. Therefore, when a reaction inhibitor of the same kind isused, the potential at which the current oscillation occurs can becontrolled by regulating the length of the carbon chain, thereby thestructure of a substance to be deposited on the surface of the workingelectrode can be determined.

An electrochemical deposition method according to a fifth aspect of theinvention is further comprising

controlling the waveform of the electrochemical oscillation byregulating a concentration of the substance.

In this aspect of the invention, by regulating the concentration of thesubstance in the solution, the potential of or the current into theworking electrode can be controlled, that is, the waveform of theelectrochemical oscillation can be controlled, and therefore thestructure of a substance to be deposited can be determined.

An electrochemical deposition method according to a sixth aspect of theinvention is a plurality of substances are dissolved in the solution inan ionic state, and

the method further comprises

determining a composition ratio of the structure by controlling thewaveform of the electrochemical oscillation.

In this aspect of the invention, when the plural substances aredissolved in the solution in the ionic state, the composition ratio ofthe structure comprised of the substances can be determined bycontrolling the waveform of the electrochemical oscillation. Forexample, when the structure comprised of the substances is deposited,the substances differ from each other in their deposition amountrelative to the potential of the working electrode according to thedifference between the degrees of their ionization tendencies. Andfurther, since the waveform of the electrochemical oscillation can becontrolled by controlling the potential of the working electrode, thecomposition ratio of the structure can be determined (controlled) bycontrolling the deposition amounts of the substances. For example, in acase where metals are used as the substances, they have a property thatwhen the potential of the working electrode has been lowered (when thepotential has been set at a lower negative value), the depositioncurrent increases, that is, the deposition amount increases; however,since the ratios of their deposition amounts to the potential differfrom each other according to the difference between the degrees of theirionization tendencies, the composition ratio can be changed.

An electrochemical deposition method according to a seventh aspect ofthe invention is characterized in that the structure of the substancedeposited according to the waveform of the electrochemical oscillationis a multilayered structure.

In this aspect of the invention, the substance having the multilayeredstructure can be deposited on the surface of the working electrode byusing the foregoing electrochemical deposition method.

An electrochemical deposition method according to an eighth aspect ofthe invention is characterized in that one of a thickness and acomposition ratio of each layer of the multilayered structure aredetermined by controlling the waveform of the electrochemicaloscillation.

In this aspect of the invention, since the potential of or the currentinto the working electrode can be controlled, that is, since thewaveform of the electrochemical oscillation can be controlled by, forexample, regulating the concentration of the substance in the solution,the deposition amount of the substance can be controlled. When amultilayer structure comprised of plural substances is produced, any oneof the thickness and the composition ratio or both of each layer can bedetermined because the deposition amount of each substance can beregulated. Specifically, the thicknesses of the layers can be determinedby regulating the concentrations of the substances together whilekeeping the ratio between the concentrations of the substances constant.

An electrochemical deposition method according to a ninth aspect of theinvention is characterized in that metals are used as the substances.

In this aspect of the invention, the metals can be deposited on thesurface of the working electrode by using the foregoing electrochemicaldeposition method.

An electrochemical deposition method according to a tenth aspect of theinvention is characterized in that the potential of or the currentthrough the working electrode is controlled such that theelectrochemical deposition proceeds under diffusion limited control togenerate the electrochemical oscillation.

In this aspect of the invention, the electrochemical oscillation isgenerated by controlling the potential of or the current into theworking electrode such that the electrochemical deposition proceedsunder the diffusion limited control. Since an electrochemical phenomenonis produced by a balance between autocatalytic crystal growth in aspecific orientation and autocatalytic surface passivation on athermodynamically stable plane, an ordered microstructure having grownin a direction perpendicular to the working electrode is formed on thesurface of the working electrode through the reflection of the historyof the electrochemical oscillation. Therefore the structure isaccumulated as a history and the trace of a dynamic space-time order canbe fixed and stored, thereby the formed structure does not vanish.

An electrochemical deposition method according to an eleventh aspect ofthe invention is further comprising:

detecting an upper or lower potential on every oscillation of theelectrochemical oscillation; and

controlling the current to the working electrode based on variations inthe detected upper or lower potentials.

In this aspect of the invention, the upper or lower potential of eachoscillation of the electrochemical oscillation is detected and thecurrent into the working electrode is controlled based on the variationin the detected upper or lower potential. The oscillation phenomenonspontaneously occurs at a certain current density which means athreshold value at which a reaction rate-determining process turns to adiffusion limiting process. However, since the effective area of theworking electrode gradually increases due to the growth of amicrostructure on the surface of the working electrode, the currentdensity gradually lowers and then falls outside a range in which thespontaneous oscillation occurs, thereby the spontaneous oscillationceases. Therefore the spontaneous oscillation can be continued bycontrolling the current into the working electrode.

An electrochemical deposition method according to a twelfth aspect ofthe invention is characterized in that the current to the workingelectrode is controlled such that an effective current density relativeto the solution is substantially constant.

In this aspect of the invention, the shapes (for example, the latticespacings) of individual microstructures growing on the surface of theworking electrode become uniform by controlling the effective currentdensity at the working electrode relative to the solution so as tobecome constant substantially, thereby a microlattice structure withsuperior evenness can be formed.

An electrochemical deposition method according to a thirteenth aspect ofthe invention is characterized in that the waveform of theelectrochemical oscillation is controlled by regulating a concentrationof the substance.

In this aspect of the invention, since a potential of or a current intothe working electrode can be controlled, that is, since the waveform ofthe electrochemical oscillation can be controlled by regulating theconcentrations of the substances in the solution, the structure of asubstance to be deposited can be determined. For example, by increasingthe ion concentrations of the substances in the solution, each structureof the periodic structure of the substance to be deposited can beincreased in size.

An electrochemical deposition apparatus according to a fourteenth aspectof the invention is an electrochemical deposition apparatus fordepositing

a substance on a surface of a working electrode by feeding a currentbetween a plurality of electrodes immersed in a solution in which thesubstance is dissolved in an ionic state and generating electrochemicaloscillation, the apparatus comprising:

a detector for detecting an upper or lower potential every oscillationof the electrochemical oscillation; and

a current control unit for controlling the current to the workingelectrode relative to the solution based on the upper or lower potentialdetected by the detector.

In this aspect of the invention, the electrodes are immersed in thesolution in which the electrochemically depositable substance (such as ametal, a semiconductor, or a conductive polymer) is dissolved in theionic state, the detecting unit detects the upper or lower potential ofeach oscillation of the electrochemical oscillation, and the controlunit controls the current into the working electrode relative to thesolution based on the detected upper or lower potential. The spontaneouselectrochemical oscillation is generated by feeding the current betweenthe electrodes, thereby the dissolved substance is electrochemicallydeposited on the surface of one electrode (the working electrode) of theelectrode. The structure of the substance to be deposited can becontrolled by controlling a current to be fed to the working electrode.

An electrochemical deposition apparatus according to a fifteenth aspectof the invention is characterized in that the current control unitcontrols the current to the working electrode, the current correspondingto a current density at which the spontaneous oscillation generates.

In this aspect of the invention, since the current to be fed to theworking electrode is controlled such that the current density at whichthe spontaneous oscillation occurs can be secured, it is possible tosolve the problem that since the current density gradually lowers andthen falls outside a range in which the spontaneous oscillation occurs,the spontaneous oscillation ceases, and therefore the spontaneousoscillation can be continued.

A microstructure according to a sixteenth aspect of the invention is amicrostructure formed by using the substance deposited by using theelectrochemical deposition method described above, wherein themicrostructure includes a three-dimensional base structure and isprovided with a deposit of another substance thereon.

In this aspect of the invention, the microstructure can be used as ahigh-strength electrode with an extremely large surface area by usingthe microstructure (for example, the microlattice structure) formedthrough the use of such a deposition method as a three-dimensional basestructure (template) and then depositing another substance (electricconductor) such as platinum on the surface of the microstructure asdescribed above. And further, the microstructure also has the advantagethat crystallographically stable planes are exposed.

A microstructure according to a seventeenth aspect of the invention is amicrostructure including an internal porous structure shaped by formingthe substance deposited by using the electrochemical deposition methoddescribed above, polymerizing another substance on a surface of thedeposited substance, and removing the deposited substance.

In this aspect of the invention, the microstructure can be produced as amicrostructure with a hollow pattern by using the microstructure (forexample, the microlattice structure) formed through the use of such adeposition method as a three-dimensional template.

EFFECTS OF THE INVENTION

According to the present invention, an ordered microstructure isspontaneously formed perpendicularly from a substrate by aself-organized oscillation phenomenon. Further, individual portions ofthe structure to be formed are laminated in order through the reflectionof the history of oscillation phenomenon. In this invention, since theelectrochemical oscillation phenomenon itself is intended to becontrolled, the ordered structure to be formed can be controlled. Andfurther, it becomes possible to form a simple periodic structure, a morecomplicated three-dimensional ordered structure, and variousmicrolattice structures on the entire surfaces of electrodes at one stepand low cost. Still further, by controlling a current fed to the workingelectrode such that a current density at which the spontaneousoscillation occurs can be secured, it becomes possible to solve theproblem that since the current density gradually lowers and then fallsoutside a range in which the spontaneous oscillation occurs, thespontaneous oscillation ceases, that is, the spontaneous oscillation canbe continued, and therefore a microlattice metal aggregate having a sizeof several millimeters to several centimeters can be formed. Stillfurther, it is also possible to form a three-dimensional orderedstructure applicable to metals, semiconductors, conductive polymers, andso on by utilizing the obtained ordered structure itself as a template.Moreover, since the ordered structure is theoretically to anelectrochemical deposition reaction of a desired substance by suitablyselecting a reaction inhibitor, it is expected that the structure willbe applied to the formation of various functional materials. Andfurthermore, the structure of an apparatus used for the electrochemicaldeposition is extremely simple, which brings great advantages such asthe capability of manufacturing a specified microstructure at extremelylow cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory drawing of an electrochemical deposition methodaccording to a first embodiment of the present invention.

FIG. 2 is a graph of current oscillation.

FIG. 3 is an explanatory drawing of an evaluation method for a thinfilm.

FIG. 4 is an electron microscope photograph of a multilayer film formedby using the electrochemical deposition method according to the firstembodiment of the invention and Auger electron spectroscopy resultsshowing the evaluation results of the film.

FIG. 5 is a graph of deposition currents for Cu and Sn relative to thepotential of a working electrode.

FIG. 6 is a graph of the correspondence between the waveform of electricoscillation and the composition ratio of a deposit.

FIG. 7 is a graph of the relationship between deposition currents andthe potential of the working electrode brought about by usingC_(X)H_(2X-1)N(CH₃)₃Cl.

FIG. 8 is a graph of the relationship between deposition currents andthe potential of the working electrode brought about by using C12TAC.

FIG. 9 is an explanatory drawing of an electrochemical deposition methodaccording to a second embodiment of the invention.

FIG. 10 is a graph of potential oscillation.

FIG. 11 is an electron microscope photograph of an example of amicrostructure formed by using the electrochemical deposition methodaccording to the second embodiment of the invention.

FIG. 12 is an explanatory drawing of a periodic structural changecorresponding to potential oscillation required for the deposition ofSn.

FIG. 13 is an explanatory drawing of a periodic structural changecorresponding to the potential oscillation required for the depositionof Sn.

FIG. 14 is a graph of the potential oscillation required for thedeposition of Sn.

FIG. 15 is an electron microscope photograph of a microstructure formedby changing a current value at a working electrode.

FIG. 16 is a graph of potential oscillation required for the depositionof Zn.

FIG. 17 is an electron microscope photograph of microstructures formedby changing the ion concentration of Zn.

FIG. 18 is a graph of the relationship between a potential and a currentdensity.

FIG. 19 is a graph of a change in the potential oscillation with respectto time.

FIG. 20 is an electron microscope photograph taken at points A and B of(a) of FIG. 19.

FIG. 21 is an explanatory drawing of the configuration of anelectrochemical deposition apparatus according to a third embodiment ofthe invention.

FIG. 22 is an explanatory drawing of the control of a current value by acontrol unit.

FIG. 23 is a graph of an example of the control of the current value bythe control unit.

FIG. 24 is an optical microscope photograph of an example of amicrostructure formed by using the electrochemical deposition apparatusaccording to the third embodiment of the invention.

DESCRIPTION OF THE REFERENCE NUMERALS

1 and 11 Positive electrodes

2 and 12 Negative electrodes (working electrodes)

3 and 13 Reference electrodes

4 and 14 Solutions

5 and 15 Liquid tanks

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below in detailwith reference to the drawings.

Embodiment 1

FIG. 1 is an explanatory drawing of an electrochemical deposition methodaccording to a first embodiment of the invention. Incidentally, in thisembodiment, a description of a case where current oscillation as oneform of electrochemical oscillation is controlled will be presented.

As shown in FIG. 1, conductive metal substrates, i.e., a positiveelectrode 1 and a negative electrode 2 are arranged oppositely in aliquid tank 5 containing an electrolytic (acid) solution (hereinafterreferred to as “solution”) 4 in which plural substances (in this case,Cu and Sn are used) are dissolved in an ionic state, and then apredetermined voltage is applied between the positive electrode 1 andthe negative electrode 2. In addition to the two electrodes 1 and 2, areference electrode 3 is also arranged in the liquid tank 5 and thepotential between the negative electrode 2 and the reference electrode 3is measured. Since the solution 4 can be considered as a conductor, thepotential V1 of the negative electrode 2 to the solution 4 can bedetermined. Furthermore, a reaction inhibitor is admixed into thesolution 4 and spontaneous electrochemical oscillation (currentoscillation in this case) is generated in the electrochemical depositionreaction of Cu and Sn in the presence of the reaction inhibitor.Examples of the reaction inhibitor include cationic surfactants; thus,Amiet-320 (chemical formula 1), C_(X)H_(2X-1)N(CH₃)₃Cl (chemical formula2), TritonX-100 (chemical formula 3), or the like can be used.Incidentally, it is preferable to admix a citric acid with the solution4 as a lubricating agent, and therefore in this embodiment, the solution4 prepared by mixing CuSO₄ at a concentration of 0.15 M, SnSO₄ at aconcentration of 0.15 M, H₂SO₄ at a concentration of 0.6 M, a citricacid at a concentration of 0.5 M, and Amiet-320 at a concentration of0.5 mA was used.

[Chemical Formula 1]

Through the admixture of the reaction inhibitor with the solution 4, anegative derivative resistance induced by the reaction inhibitor and apotential drop in the solution couple with each other, which effects anautocatalysis process. When the potential V1 of the negative electrode 2is in a predetermined range, minor fluctuations in the concentrations,temperature, and so on are amplified due to the autocatalysis process,thereby the current oscillation occurs as macroscopic and periodicoscillation shown in FIG. 2.

To be more specific, since the solution 4 can be considered as aconductor, ions on the surface of the negative electrode 2 are subjectedto a strong electric field, thereby dehydration occurs and the ions turnto absorbing atoms through the reception of electrons from the negativeelectrode 2. The absorbing atoms diffuse on the surface of the negativeelectrode 2 and a point at which crystal lattices are formed is reached,thereby a crystal is formed. The attachment and detachment of thereaction inhibitor to and from the negative electrode 2 occuralternately and spontaneously and the oscillation phenomenon occurs withthe attachment and detachment of the reaction inhibitor. In thisembodiment, the negative electrode 2 functions as a working electrodeand a thin film comprised of Cu and Sn and having superior smoothnessdeposits on the surface of the negative electrode 2 based on thewaveform of the generated oscillation. Incidentally, the smoothnessresults from the admixture of the citric acid, and therefore in a casewhere the admixture is not done, asperities are left on the surface ofthe film.

Next, the grown film was evaluated for it properties. FIG. 3 is anexplanatory drawing of a method for evaluating the film for itsproperties. To begin with, the surface of a sample 20 made by growingthe thin film 21 was subjected to an Ar etching process with the sample20 rotated (see FIG. 3(a)) to make a conical hole in the thin film 21(see FIG. 3(b)). By observing the thin film 21 thus formed from abovethrough the use of an electron microscope, it was confirmed that thereare concentric light and dark portions as shown in FIG. 4(a); that is,it was confirmed that the grown thin film has a multilayer structure.And furthermore, the side of the thin film (multilayer film) wasanalyzed by means of scanning Auger spectroscopy in order to evaluatethe composition ratio of the multilayer film, and thereupon it wasconfirmed that the composition ratio periodically changes as shown inFIG. 4(b).

The multilayer film is grown on the surface of the negative electrode 2and hence, by shaping the negative electrode 2 into, for example, acylinder, a multilayer film having superior smoothness can be formedinside the cylinder. According to the electrochemical deposition methodof this embodiment, deposits can be grown on the surfaces of electrodesindependently of the shapes of the electrodes, and therefore no matterhow their shapes are, multilayer films having superior smoothness can beformed on their surfaces. Put another way, through the use of anelectrode desirably shaped in advance and the application of theelectrochemical deposition method according to the invention, amultilayer film having the desirable shape can be formed on the surfaceof the electrode.

In the invention, the thin film (an alloy of Cu and Sn) is depositedthrough the generation of the current oscillation as the multilayer filmas described above, and the composition ratio and thickness of themultilayer film and the number of the layers (the number of times thelamination process is performed) are regulated as described below.

<1. Potential of Negative Electrode>

With respect to the potential of the negative electrode (workingelectrode) where the current oscillation occurs, there is the range ofits regulation; therefore, through the regulation of the potential ofthe working electrode, the waveform of the current oscillation can becontrolled, which makes it possible to regulate the composition ratio ofthe multilayer film and the thicknesses of the layers. That is, one goodway to form the multilayer film with a desired composition ratio is toregulate the potential of the working electrode. The potential of theworking electrode can be set at a desired value by changing a voltageapplied between the positive electrode 1 and the negative electrode 2.

FIG. 5 is a graph of deposition currents for Cu and Sn relative to thepotential of the working electrode. The deposition currents for Cu andSn are each increased by lowering the potential of the working electrode(by using a lower negative potential), and the deposition current for Snis generated at a lower negative potential as compared with that for Cu.Therefore, by making the setting of the deposition apparatus such thatthe current oscillation is generated in a state in which the potentialof the working electrode is high, the deposition amount of Sn can bemade less than that of Cu, that is, the composition ratio of Cu(Cu/(Cu+Sn)) can be increased. In contrast, by making the setting of thedeposition apparatus such that the current oscillation is generated in astate in which the potential of the working electrode is low, thecomposition ratio of Cu can be lowered. In other words, the compositionratio of the deposit can be controlled by regulating the potential ofthe negative electrode according to the difference between the degreesof the ionization tendencies of the substances in the solution. Forexample, a multilayer film can be formed by alternately laminatinglayers comprised of Cu₂Sn₈ and layers comprised of Cu₇Sn₃.

Moreover, through the regulation of the potential of the workingelectrode, the waveform (for example, the cycle) of the currentoscillation is controlled, thereby the thicknesses of the layers can beregulated. For example, the thicknesses of the layers can be increasedby lowering the potential of the working electrode; the thicknesses canbe decreased by increasing the potential.

<2. Concentrations of Substances in Solution>

The deposition current can be regulated by regulating the concentrationsof the substances contained in the solution, and therefore thecomposition ratio of the thin film can be determined (controlled) byregulating the amount of the deposited substances. For example, thecomposition ratio of Cu can be increased by increasing the concentrationof Cu.

Furthermore, the thicknesses of the layers can be regulated byregulating the concentrations of Cu and Sn together without changing theconcentration ratio between Cu and Sn. FIGS. 6(a) and 6(b) are each agraph of the correspondence between the waveform of the electricoscillation and the composition ratio of the deposit. In FIG. 6(a), theconcentrations of CuSO₄ and SnSO₄ are 0.15 M and in FIG. 6(b), theirconcentrations are 0.10 M. The period of the oscillation can beshortened by lowering the concentrations, and thus a multilayer filmhaving a thickness corresponding to the period of the oscillation can bedeposited. For example, in this embodiment, when the concentrations are0.15 M, the layers each having a thickness of 90 nm are deposited andwhen the concentrations are 0.10 M, the layers each having a thicknessof 38 nm are deposited.

<3. Kind and Concentration of Reaction Inhibitor>

When the reaction inhibitor has attached to one place of the substratedue to the fluctuations, the species spreads over the surface of thenegative electrode with its phases uniform by virtue of itsautocatalysis function, thereby the deposit accumulates on the entiresurface of the negative electrode. Since the potential of the negativeelectrode to which the reaction inhibitor attaches is determined by thekind and concentration of the reaction inhibitor, the potential at whichthe current oscillation occurs, that is, the waveform of the currentoscillation can be controlled by selecting the kind of the reactioninhibitor and by regulating its concentration.

When the above compound C_(x)H_(2x-1)N(CH₃)₃Cl was used, it wasconfirmed that the compound functions as a reaction inhibitor only whenthe compound has a carbon chain comprised of 10 carbon atoms (C10) ormore, that is, only when its composition parameter X is 10 (C10TAC), 12(C12TAC), or 16 (C16TAC).

The relationship between the kind of the reaction inhibitor and thepotential at which the current oscillation occurs was evaluated by usinga solution 4 prepared by mixing C_(x)H_(2x-1)N(CH₃)₃Cl having a carbonchain composed of 10, 12, or 16 carbon atoms at a concentration of 5 mMinto a solution comprised of CuSO₄ at a concentration of 0.15 M, SnSO₄at a concentration of 0.15 M, H₂SO₄ at a concentration of 0.5 M, and acitric acid at a concentration of 0.5 M.

FIG. 7 is a graph showing the relationship between the depositioncurrent and the potential of the working electrode brought about byusing C_(x)H_(2x-1)N(CH₃)₃Cl. FIG. 7(a) shows the case where C10TAC iscontained in the solution as the reaction inhibitor, FIG. 7(b) shows thecase where C12TAC is contained therein, and FIG. 7(c) shows the casewhere C16TAC is contained therein. The current oscillation occurs basedon the potential level of the negative derivative resistance andtherefore, when reactive inhibitor of the same kind are used, thepotential at which the current oscillation occurs can be shifted to thepositive side by using the reaction inhibitor having a longer carbonchain. Therefore, by regulating the length of the carbon chain of thereaction inhibitor, the potential at which the current oscillationoccurs can be controlled, that is, the waveform of the currentoscillation can be controlled, which makes it possible to form amultilayer film having a structure corresponding to the level of thecurrent oscillation.

The relationship between the concentration of the reaction inhibitor andthe potential at which the current oscillation occurs was evaluated byusing a solution 4 prepared by mixing C12TAC with a concentration whichis not the same as that described above into a solution comprised ofCuSO₄ at a concentration of 0.15 M, SnSO₄ at a concentration of 0.15 M,H₂SO₄ at a concentration of 0.25 M, and the citric acid at aconcentration of 0.5M.

FIG. 8 is a graph showing the relationship between the depositioncurrent and the potential of the working electrode brought about byusing C12TAC. FIG. 8(a) shows the case where the concentration of C12TACis 2 mM, FIG. 8(b) shows the case where the concentration of C12TAC is 3mM, and FIG. 8(c) shows the case where the concentration of C12TAC is 4mM. The current oscillation occurs based on the potential level of thenegative derivative resistance and therefore, when reaction inhibitor ofthe same kind are used, the potential at which the current oscillationcan be shifted to the positive side by using the reaction inhibitor witha higher concentration. Accordingly, through the regulation of theconcentration of the reaction inhibitor, the potential at which thecurrent oscillation occurs can be controlled, that is, the waveform ofthe current oscillation can be controlled, which makes it possible toform a multilayer film having a structure corresponding to the level ofthe current oscillation.

As described in detail above, according to the electrochemicaldeposition method according to the first embodiment, the multilayer filmcan be formed on the entire surface of the working electrode at one stepand low cost. And further, the method can be theoretically applied toelectrochemical deposition reactions of not only metals butsemiconductors (such as Cu₂O), conductive polymers (such aspolyaniline), and so on by suitably selecting the reaction inhibitor, itis expected that the method will be applied to the production of variousfunctional materials. Furthermore, the structure of an apparatus usedfor the deposition is extremely simple, and thus a specifiedmicrostructure can be manufactured at extremely low cost.

In the embodiment of the invention, the description of the case wherethe alloy of Cu and Sn is made by using the mixed solution containing Cuand Sn; however, materials which can be used are not limited to such analloy. Multilayer films are also formed by the electrochemicaldeposition reaction of Cu in a solution into which phenanthrene (C₁₄H₁₀)acting as a reaction inhibitor is mixed, the electrochemical depositionreaction of Ni in a solution into which a hypophosphorous acid(H₂PO(OH)) is mixed, and so on, and therefore the electrochemicaldeposition method according to the invention is available to reactionsystems in which electric oscillation occurs. Accordingly, ahigh-quality multilayer structure can be easily formed by using adesired material; for example, it becomes possible to easily producedevices having functions based on multilayer structures such as giantmagnetoresistance and tunneling magnetoresistance at low cost.

Moreover, in this embodiment, the description of the current oscillationhas been presented as one form of electrochemical oscillations; inaddition, it is needless to say that potential oscillation (theoscillation of the potential of the working electrode) can also beutilized, that is, an oscillation phenomenon can be produced bycontrolling the amount of current to be fed to the working electrode.

Embodiment 2

In the first embodiment, the oscillation phenomenon is produced bymixing the reaction inhibitor into the solution to couple the negativedifferential resistance induced by the reaction inhibitor with thepotential drop of the solution. On the other hand, the potential of orthe current into a working electrode can be controlled such that thedeposition of substances dissolved in a solution onto the surface of theworking electrode proceeds under the diffusion limited control of thesubstances; a description of such a method will be presented below as asecond embodiment, that is, a method for forming a lattice structure onthe surface of a working electrode through the control of potentialoscillation will be described below.

FIG. 9 is an explanatory drawing of the electrochemical depositionmethod according to the second embodiment of the invention.Incidentally, in this embodiment, a description of a case wherepotential oscillation as one form of electrochemical oscillations iscontrolled will be presented.

As shown in FIG. 9, conductive metal substrates, i.e., a positiveelectrode 11 and a negative electrode 12 are oppositely arranged in aliquid tank 15 containing an electrolytic solution (hereinafter referredto as “solution”) 14 in which substances (in this case, metals such asSn and Zn are used) are dissolved in an ionic state, and then apredetermined current is fed between the negative electrode 12 and thepositive electrode 11; that is, a constant current source is connectedbetween the negative electrode 12 and the positive electrode 11.Incidentally, the value of an output current from the constant currentsource can be set suitably. And further, in addition to the twoelectrodes 11 and 12 described above, a reference electrode 13 isarranged in the liquid tank 15 and a potential between the referenceelectrode 13 and the negative electrode 12 is measured. Since thesolution 14 can be considered as a conductor, a potential V2 of thenegative electrode 12 relative to the solution 14 can be determined. Bycontrolling the current such that the proceeding toward the diffusioncontrol of the substances is done under diffusion-controlling conditionsin the electrochemical deposition reaction of the substances,spontaneous electrochemical oscillation (in this case, potentialoscillation) occurs. Incidentally, in this embodiment, the solution 14containing Sn²⁺ at a concentration of 0.2 M and NaOH at a concentrationof 4 M was used.

By controlling the current such that the proceeding toward the diffusioncontrol is done, an autocatalysis process is produced. When a currentvalue between the negative electrode 12 and the positive electrode 11falls within a predetermined range, minor fluctuations are amplified bythe autocatalysis process, thereby potential oscillation shown in FIG.10 occurs as macroscopic and periodic oscillation.

Since the oscillation phenomenon is produced by a balance betweenautocatalytic crystal growth along a specific orientation andautocatalytic surface inactivation on a thermodynamically stable plane,the crystals of the substances grow in a direction perpendicular to theworking electrode through the reflection of the history of the potentialoscillation, thereby an ordered microstructure is formed on the surfaceof the negative lo electrode 12 which functions as a working function.When Sn and Zn are used as the substances, Sn is deposited such that alattice structure is formed as shown in FIG. 11(a) and Zn is depositedsuch that a structure in which hexagonal plates overlap one afteranother is formed as shown in FIG. 11(b). It is needless to say that thekinds of the substances are not limited to them; Pb is used, a micronetwork structure is formed three-dimensionally. Therefore the structureof a substance to be deposited depends on the crystal structure of thesubstance itself to be deposited.

In order to evaluate how the waveform of the potential oscillation isreflected by the lattice structure, the negative electrode (workingelectrode) 12 was pulled up from the solution 14 at several potentialsat which the potential oscillation occurs to observe the surface of theworking electrode through the use of an electron microscope and anoptical microscope.

FIGS. 12 and 13 are explanatory drawings of periodical changes in thestructure of Sn synchronizing to potential oscillation required for thedeposition of Sn. FIG. 12(a) shows the waveform of the potentialoscillation required for the deposition of Sn, FIG. 12(b) shows crystalplanes and orientations of Sn, and FIG. 13(a), 13(b), and 13(c) are thescanning electron microscope (SEM) photographs, optical microscope (OM)photographs, and schematic depictions of the surface of the negativeelectrode observed at the potentials A, B, C shown in FIG. 12(a).Incidentally, the amount of current from the constant current source wasset such that the density of the current fed between the negativeelectrode 12 and the positive electrode 11 is −36 mA/cm².

At the negative end of the potential oscillation (potential A of FIG.12(a)), angular Sn crystals were found and further, it was observed thata (110) plane and a (011) plane as thermodynamically stable orientationplanes are exposed at the individual crystals (see FIG. 13(a)). When thepotential has risen from the negative end (potential B of FIG. 12(a)),it was observed that needle-shaped Sn crystals deposit from the cornersof the angular Sn crystals in <101> directions (see FIG. 13(b)). Andfurther, at the potential of the positive end (potential C of FIG.12(a)), it was observed that the thermodynamically stable planes of thetips of the needle-shaped Sn crystals are exposed again to initiatecrystallization (see FIG. 13(c)). It was clear from the observationresults that a lattice structure with a desired shape can be formed bycontrolling the waveform of the potential oscillation.

Next, a method for controlling the waveform of the potential oscillationwill be described below.

<1. Current Value of Working Electrode>

FIG. 14 is a graph of the potential oscillation required for the 5deposition of Sn; the horizontal axis indicates the lapse of time, andthe vertical axis indicates the potential of the working electrode.

FIG. 14 shows the potential oscillation generated when a constantcurrent of −12 mA has been fed between the working electrode, i.e., thenegative electrode 12 and the positive electrode 11 up to 62 seconds anda constant current of −20 mA has been fed between the negative electrode12 and the positive electrode 11 after that. It is apparent that thewaveform of the potential oscillation changes by changing the value ofthe current, that is, after the lapse of 62 seconds. Incidentally, thepotential oscillation is unstable up to 42 seconds because the reactionis unstable.

With respect to such a structure formed by changing the current value ofthe working electrode, the structural parameter of lattices to be formedcan be controlled as shown in FIG. 15. That is, in the method fordepositing the crystal of Sn according to the embodiment, latticespacings can be changed by changing the current value. In thisembodiment, it is apparent that since the current value was changedduring the crystal growth, the lattice spacings changed from a crystal Cdeposited at the point in time when the current value was changed.

That is, with respect to the current value at which the potentialoscillation occurs, there is the range of its regulation; therefore,through the regulation of the current value, the waveform of thepotential oscillation can be controlled, thereby the structuralparameter of a structure to be formed can be controlled.

<2. Concentrations of Substances in Solution>

The relationship between the concentration of the substance and thewaveform of potential oscillation was evaluated by using a solution 14containing Zn²⁺ at a concentration which is not the same as thatdescribed above and NaOH at a concentration of 4 M.

FIG. 16(a), 16(b), and 16(c) are graphs of potential oscillationsthrough which the deposition of Zn was brought about and theirhorizontal axes indicate lapses of time. FIG. 16(a) shows a potentialproduced when the ion concentration of Zn is 0.1 M, FIG. 16(b) shows apotential produced when the concentration is 0.2 M, and FIG. 16(c) showsa potential produced when the concentration is 0.5 M. The period of theoscillation can be lengthened by increasing the ion concentration of Zn.FIGS. 17(a), 17(b), and 17(c) are electron microscope photographs ofmicrostructures formed when the ion concentration of Zn was changed.FIG. 17(a) shows the case where the ion concentration of Zn is 0.1M,FIG. 17(b) shows the case where the ion concentration of Zn is 0.2 M,and FIG. 17(c) shows the case where the ion concentration of Zn is 0.5M, from which it is apparent that the size of hexagonal plates can beincreased by increasing the ion concentration.

That is, the waveform of the potential oscillation can also becontrolled by regulating the concentration of the substance contained inthe solution, and therefore the structural parameter of a structure tobe formed can be controlled as described above.

As described in detail above, according to the electrochemicaldeposition method of the second embodiment, the microstructures inherentin the substances deposited can be formed on the entire surface of theworking electrode at one step and low cost. And further, since thestructure of the apparatus used for the deposition is extremely simple,a specified microstructure can be produced at extremely low cost.

In this embodiment, the description of the potential oscillation hasbeen presented as one form of electrochemical oscillations; in addition,it is needless to say that such deposition can also be produced by meansof current oscillation (the oscillation of current at the workingelectrode), that is, an oscillation phenomenon can be produced bycontrolling the potential of the working electrode.

Incidentally, in the potential oscillation as one form ofelectrochemical oscillations, when the current density is below athreshold value jdl (ca. −25 mA/cm²), the potential spontaneously startsto oscillate as shown in FIG. 18. Put another way, when the currentdensity is low, the electrochemical oscillation does not occur, andtherefore it can be said that the threshold value jdl is a boundary atwhich the reaction rate-determining process turns to the diffusionlimiting process. That is, in order to continue the potentialoscillation, it is extremely important to maintain the diffusionlimiting process through the control of the current density.

FIGS. 19(a) and 19(b) are graphs each showing a change in the potentialoscillation with respect to time; the horizontal axes indicate thelapses of times and the vertical axes indicate potentials. FIG. 19(a)shows the case where the constant current is fed between the workingelectrode (i.e., the negative electrode 12) and the positive electrode11; in that case, the potential oscillation ceases after a lapse ofabout 250 seconds (which corresponds to about 75 times in terms of thenumber of the cycles of the oscillation). This is because the effectivearea of the working electrode gradually increases through the growth ofthe microstructure on the surface of the working electrode and then thecurrent density gradually lowers and deviates from the region where thespontaneous oscillation occurs. And furthermore, since the currentdensity lowers each time the growth is repeated as shown in FIG. 20, thelattice spacings of the microstructure growing on the surface of theworking electrode gradually shortens, thereby the evenness of themicrostructure is impaired. Incidentally, FIGS. 20(a) and 20(b) areelectron microscope photographs taken at the points A and B of FIG.19(a) respectively.

Therefore, as shown in FIG. 19(b), it is preferable to continue thespontaneous oscillation through the keeping of the effective currentdensity done by considering an increase in the effective electrode areaand controlling (gradually increasing) the current fed between theworking electrode (i.e., the negative electrode 12) and the positiveelectrode 11 so as to cancel out the effect of the increase in the area.

Embodiment 3

FIG. 21 is an explanatory drawing of the structure of an electrochemicaldeposition apparatus according to a third embodiment of the invention.Incidentally, in this embodiment, a description of the control ofpotential oscillation as one form of electrochemical oscillations willbe presented.

In the electrochemical deposition apparatus according to the thirdembodiment of the invention, the conductive metal substrates, i.e., thepositive electrode 11 and the negative electrode 12 are oppositelyarranged in the liquid tank 15 containing the electrolytic solution(hereinafter referred to as “solution”) 14 in which substances (in thiscase, metals such as Sn and Zn are used) are dissolved in an ionic stateand a current is fed between the negative electrode 12 and the positiveelectrode 11. And further, in addition to the two electrodes 11 and 12,the reference electrode 13 is arranged in the liquid tank 15.Furthermore, the deposition apparatus is provided with a detecting unit16 which measures a potential between the reference electrode 13 and thenegative electrode 12 and which detects an upper potential or a lowerpotential at each oscillation of the electrochemical oscillation and acontrol unit 10 which controls a current to the working electroderelative to the solution based on the upper or lower potential detectedby the detecting unit 16. Since the solution 14 can be considered as aconductor, the potential V2 of the negative electrode 12 relative to thesolution 14 is determined, and then the control unit 10 controls acurrent to be fed between the negative electrode 12 and the positiveelectrode 11 base on the potential V2. Specifically, a constant currentsource is connected between the negative electrode 12 and the positiveelectrode 11 and the control unit 10 controls the value of a current fedfrom the constant current source. In this case, the term upper potentialrefers to an extreme value in the positive direction (maximum value) ofthe oscillation, and the term lower potential refers to an extreme valuein the negative direction (minimum value) of the oscillation.

FIG. 22 is an explanatory drawing of the control of a current value bythe control unit.

FIG. 22(a) shows a potential waveform generated when the potentialoscillation occurs; reference letter A denotes an nth oscillationwaveform, reference letter B denotes an n+1th oscillation waveform, andreference letter C denotes an n+2th oscillation waveform. Since themicrostructure grows at the working electrode through the potentialoscillation as described above, the effective electrode area increasesand the upper and lower potentials of the potential oscillation aredisplaced in the negative direction every cycle. And further, when acurrent I has been fed, a potential loss expressed by the Ohm's law I×R(R is the resistance of the solution) is produced. That is, as shown inFIG. 22(b), a potential loss is produced by the increase in theelectrode area ΔA in the process of the crystal growth from the nthgeneration to the n+1th generation. The current I is proportional to theelectrode area A, i.e., the equation I=k×A holds, and an increase in thepotential loss is expressed by a product (k∴ΔA)×R. In addition, thedisplacement ΔU of the upper potential and the lower potential at thepotential oscillation (hereinafter exemplified by using the upperpotential) is expressed by the following equation:ΔU=(k×ΔA)×R   (equation (1))

A current density j can be defined as follows:

j=I/A (where I is the current value and A is the effective electrodearea). In the process of the nth-generation crystal growth, the currentdensity jn is expressed by the equation jn=In/An and in the process ofthe n+1th-generation crystal growth, the current density jn+1 isexpressed by the equation jn+1=(In+ΔI)/(An+ΔA); therefore, in thisembodiment, since ΔI is controlled such that jn=n+1, the equationIn/An(In+ΔI)/(An+ΔA) holds, from which the following equation isderived:ΔI=In/An×ΔA   (equation (2))

From the equations (1) and (2), the equation ΔI=jn×(U/(k×R)) is derived.And further, since j0=j1= . . . jn, the following equation is derived:ΔI=j0×(ΔU/(k×R))   (equation (3))where k×R is a parameter dependent upon experimental system includingthe location of the electrodes and the concentrations of the substancesand takes on a constant value. Therefore, after the detection of ΔU, ΔIis calculated from equation (3) based on ΔU to control the value of thecurrent to be fed between the negative electrode 12 and the positiveelectrode 11, thereby the waveform of next-generation potentialoscillation is controlled.

FIG. 23 is a graph of an example of the control of the current value bythe control unit; the horizontal axis indicates a lapse of time, and thevertical axis indicates the value of a current fed between the workingelectrode (i.e., the negative electrode 12) and the positive electrode11. From FIG. 23, it can be seen that the value of the current fedbetween the working electrode (i.e., the negative electrode 12) and thepositive electrode 11 is increased with the lapse of time. This isbecause the increase in the effective electrode area was taken intoconsideration and the current value was gradually increased so as tocancel out the effect of the increase in the effective electrode area,whereby the effective density of the current does not vary, which allowsthe spontaneous oscillation to continue. Therefore, even when about 250seconds have elapsed, the potential oscillation does not cease. In thisembodiment, it was confirmed that even when about 2000 seconds or more(about 600 cycles in terms of the cycles of the oscillation) haveelapsed, the potential oscillation continues.

Furthermore, even when the potential oscillation has been repeated, thecurrent density remains the same, and therefore the lattice spacings ofthe microstructure growing on the surface of the working electroderemains the same as those of the microstructure formed at the time ofthe start of the oscillation, whereby the microlattice structure withsuperior evenness can be formed. As mentioned above, the microstructurewith the uniform lattice spacings can be manufactured at low cost byconsidering the increase in the effective electrode area and graduallyincreasing the current value so as to cancel out the effect of theincrease in the area with the lapse of time. And further, although thelattices range in size from several tens to several hundreds ofmicrometers, a metal microlattice aggregate having a size of severalmillimeters to several centimeters can be obtained by using theelectrochemical deposition method according to this embodiment as shownin FIG. 24.

As a result, a bulk material having such a microstructure can beobtained and therefore used as a new bulk material for an electrode. Themicrolattice structure itself of Sn is of limited application; however,a high-strength electrode with an extremely wide surface area can beproduced by using the microstructure (for example, the microlatticestructure) as a three-dimensional base structure (template) and platingthe surface of the microstructure with an electric conductor such asplatinum. And furthermore, the bulk material has the advantage thatcrystallographically stable surfaces are exposed. It is needless to saythat materials used as the coating on the microstructure can be selectedaccording to the use of the structure and it can be therefore consideredto use copper oxide except for platinum.

On the other hand, a microstructure with a hollow pattern can beproduced by using the microstructure (for example, the microlatticestructure) described in each embodiment as a three-dimensional template.For example, a polymeric substance having a hollow structure (ants'nest-shaped structure) can be produced by putting the microstructureproduced using the deposition method according to each embodiment in apolymer solution to polymerize them and then removing (etching) Snthrough the use of an etchant such as hydrochloric acid. Since such apolymeric substance has a porous structure, its application to a filtercan be expected. And further, since the lattice spacings can beregulated by controlling the waveform of the electrochemicaloscillation, it is also possible to make the polymeric substance haveplural structures whose lattice spacings are different.

In the third embodiment, an upper or lower potential of each oscillationof the electrochemical oscillation is detected and the control unit 10controls a current to be fed between the negative electrode 12 and thepositive electrode 11 based on the upper or lower potential; inaddition, a current into the working electrode relative to the solutioncan be controlled by calculating the period of each oscillation of theelectrochemical oscillation from the upper or lower potential andsecuring a current density at which the spontaneous oscillation occursbased on the calculated period.

Up to this point the electrochemical deposition method according to thepresent invention has been described with reference to the specificembodiments; however, the invention is not limited to these embodiments.Those skilled in the art will appreciate that various modifications orimprovements can be made to the structures and functions described inthe embodiments of the invention without departing from the sprit andscope of the invention.

1-17. (canceled)
 18. An electrochemical deposition method for depositingan electrochemically depositable substance on a surface of a workingelectrode by applying a voltage or feeding a current between a pluralityof electrodes immersed in a solution in which the substance is dissolvedin an ionic state, the method comprising: generating electrochemicaloscillation by controlling a potential of or the current through theworking electrode relative to the solution; and depositing the substancewith a predetermined structure according to a waveform of theelectrochemical oscillation.
 19. The method according to claim 18,further comprising: mixing a reaction inhibitor into the solution; andgenerating a state in which the reaction inhibitor attaches to thesurface of the working electrode and a state in which the reactioninhibitor detaches therefrom spontaneously and alternately.
 20. Themethod according to claim 18, further comprising controlling thewaveform of the electrochemical oscillation by regulating aconcentration of the substance in the solution.
 21. The method accordingto claim 18, wherein a plurality of substances are dissolved in thesolution in an ionic state, and the method further comprises determininga composition ratio of the structure by controlling the waveform of theelectrochemical oscillation.
 22. The method according to claim 18,wherein the structure of the substance deposited according to thewaveform of the electrochemical oscillation is a multilayered structure.23. The method according to claim 18, wherein a metal is used as thesubstance.
 24. The method according to claim 18, wherein the potentialof or the current through the working electrode is controlled such thatthe electrochemical deposition proceeds under diffusion limited controlto generate the electrochemical oscillation.
 25. The method according toclaim 19, wherein the potential of or the current through the workingelectrode is controlled by regulating a concentration of the reactioninhibitor such that the electrochemical oscillation generates.
 26. Themethod according to claim 19, wherein a cationic surfactant having acarbon chain consisting of 10 carbon atoms or more is used as thereaction inhibitor, and the potential of or the current into the workingelectrode is controlled by regulating a length of the carbon chain suchthat the electrochemical oscillation generates.
 27. The method accordingto claim 22, wherein one of a thickness and a composition ratio of eachlayer of the multilayered structure are determined by controlling thewaveform of the electrochemical oscillation.
 28. The method according toclaim 24, further comprising: detecting an upper or lower potential onevery oscillation of the electrochemical oscillation; and controllingthe current to the working electrode based on variations in the detectedupper or lower potentials.
 29. The method according to claim 28, whereinthe current to the working electrode is controlled such that aneffective current density relative to the solution is substantiallyconstant.
 30. The method according to claim 24, wherein the waveform ofthe electrochemical oscillation is controlled by regulating aconcentration of the substance in the solution.
 31. An electrochemicaldeposition apparatus for depositing a substance on a surface of aworking electrode by feeding a current between a plurality of electrodesimmersed in a solution in which the substance is dissolved in an ionicstate and generating electrochemical oscillation, the apparatuscomprising: a detector for detecting an upper or lower potential everyoscillation of the electrochemical oscillation; and a current controlunit for controlling the current to the working electrode relative tothe solution based on the upper or lower potential detected by thedetector.
 32. The apparatus according to claim 31, wherein the currentcontrol unit controls the current to the working electrode, the currentcorresponding to a current density at which the spontaneous oscillationgenerates.
 33. A microstructure formed by using the substance depositedby using the electrochemical deposition method according to claim 18,wherein the microstructure includes a three-dimensional base structureand is provided with a deposit of another substance thereon.
 34. Amicrostructure including an internal porous structure shaped by formingthe substance deposited by using the electrochemical deposition methodaccording to claim 18, polymerizing another substance on a surface ofthe deposited substance, and removing the deposited substance.